Hi, you've come to the right place!
In the UK, a new slave cylinder for the 1.2 Panda costs about £130 if you buy from a Fiat dealer or £25 if you get an aftermarket one (usually made by LUK). The LUK one is fine so no real need to buy a genuine Fiat part. Both come complete pre-filled with hydraulic fluid and the pre-formed section of pipework.
There's a lot of experience of clutch slave cylinder issues on this forum and most people will tell you that if your slave cylinder needs replacing, the master cylinder won't be far behind it. Could I strongly recommend that you change both at once. The whole job will take about 45 minutes (including removing the battery and battery tray etc.). The reason is that the two parts are connected together with a quick release hydraulic fitting which seldom comes apart without damage if the car is a few years old. Unfortunately the master cylinder is expensive at about £170 from Fiat or £150 ish aftermarket LUK. Both come complete with prefilled reservoir and pre-formed pipes as well as the quick disconnect hydraulic connector.
If you do change just the slave, you'll experience a certain amount of frustration bleeding the air out of the system. Gravity bleed seems to work the best but if you let air locks develop in the pipework while you have the fittings apart you'll likely need a pressure bleed. Again, I strongly recommend you avoid all this hassle and just change both master and slave at the same time. It's really worth it in the long run.
For the handbrake problem, there's nothing special about the Panda rear brakes. Whilst the handbrake cable has an adjuster in the car under the centre console on the floor just behind the front seats you really need to have someone look inside the brake drums and make sure all is well in there before attempting to adjust the cables. The brakes have annoyingly flimsy ratchet style self adjusters which are very expensive if bought separately. My tip would be to buy a full kit including rear shoes, wheel cylinders, adjusters and retaining springs from a supplier like Pagid. In the UK you can get these kits for about £50 from ebay and other suppliers. I'd also suggest you make life easy for yourself by removing the rear wheel bearing/hub assembly before fitting the new brakes. Get a couple of new rear hub nuts from Fiat dealer as you'll need to replace them when you re-assemble.
